HEWLETT-PACKARD
JOURNAL
T E C H N I C A L
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Vol. 8, No. 7
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LISHED CALIFORNIA THE HEWLETT-PACKARD COMPANY, 275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA
MARCH, 1957
A Fast Digital Recorder
with Analog Output for Automatic Data Plotting
FIG. 1 shows a new digital device which
considerably increases not only the speed
and amount of information that can be ob
tained with electronic frequency counters but
also the ease with which it can be obtained.
This new instrument is a high-speed digital
recorder which converts electronic counter
readings into printed form on adding machine
tape.
The new recorder is distinguished by four
special features:
1. It is fast. Print-outs can be made at rates up
to 5 lines per second.
2. It has high count capacity: numbers of as
many as 11 columns can be printed on each
line. This high count capacity enables addi
tional data such as time signals or the read
ings of more than one counter to be printed
simultaneously through use of suitable aux
iliary equipment.
Fig. 1. New -hp- Model 560 A Digital Recorder prints
-Hp- electronic counter readings on paper tape at rates
up to 5 lines per second and up to 11 columns per
line. An important feature of the instrument is that it
provides output voltages proportional to the counter
reading so that counter readings can be simultaneously
and automatically plotted by strip recorders.
P R I N T E D
I N
3. It is a slave to the counter. Counter readings
are thus reproduced exactly.
4. It has an analog output for operating a con
ventional strip-chart recorder. This feature
is an outstanding convenience in many ap
plications since it means that data can be
automatically plotted as it is received by the
counter. Further, a scale expansion feature
enables the resolution of chart recordings
made with this arrangement to be unusually
high — if desired, variations as small as 1
unit of the counted quantity can easily be
discerned in a typical recording. Where large
samples are counted, resolutions up to 1 part
in 107 can thus be obtained. Under some cir
cumstances resolutions of 1 part in 109 can
be obtained.
Fig. 2 shows how a typical tape record ap
pears as it comes from the new recorder. The
second part of the illustration shows how this
same information appears when use is made of
Fig. 2. (a) Curve of accuracy of power
line frequency made by operating strip
recorder from analog output of the new
•hp- 560A Digital Recorder which oper
ated from -hp- 524B counter (measuring
10-period averages), (b) at right shows
section of printed tape corresponding to
part of plotted curve (j actual size).
U . S . A .
C O P Y R I G H T
© Copr. 1949-1998 Hewlett-Packard Co.
1 9 5 7
H E W L E T T - P A C K A R D
C O .
198.300MC
198.200MC
Fig. 3. Curve of warm-up
characteristic of oscillator
operating near 200 me.
Curve made by operating.
198.141590 MC strip recorder from new
(FROM DIGITAL digital recorder and -hpRECOfiDERTAPE)524B with 525B con
verter.
198.200 MC
1MIN
the recorder's analog output to make
a strip record. In this illustration
there are two special features worthy
of comment. One is that where only
the last two or three places of the
measured quantity are varying, a
strip record is obtained which is
equivalent to that obtainable only
by involved arrangements such as
heterodyning with a local oscillator
to translate small frequency vari
ations to a convenient region. The
second is that the use of the analog
recorder substantially compresses
the tape data, since as many as sev
eral hundred measurements can be
plotted per lineal inch of the strip
record. The value of these features
is apparent for such work as tele
metering, systems records, fuel flow
monitoring, frequency drift meas
urements, and proof of performance
measurements.
the counter reading. The whole
scanning and printing action is
rapid: it requires only 0.2 second.
New counts can be made by the
counter during the last 20% of this
interval, so that print-outs can be
made at rates up to 5 lines (55 digits)
per second.
Although the recorder has been
designed to be capable of printing
1 1 columns, this number of columns
is seldom needed when a single
counter is involved. The recorder is
thus normally supplied with cir
cuitry for 6 wheels, as described la
ter. Where desired, however, the 11column capacity can be used with
auxiliary equipment to print the
readings of two or three counters
simultaneously or to print coded in
formation such as time along with
a counter reading.
RECORDER OPERATION
Two sets of analog output ter
minals are provided on the recorder
so that either low-impedance or
high-impedance type strip recorders
can be used. A special feature of
these outputs is that the voltages
provided are proportional to the
total represented by any three adja
cent columns or the right-hand two
columns of the print-out. This fea
ture permits much higher resolution
to be obtained in a typical strip re
cording than with other methods
since it gives an expanded scale type
recording. Consider, for example, a
The printing mechanism in the
new recorder operates from the volt
age staircases developed in each dec
ade unit (display column) of -hpfrequency counters. These staircases
are applied to comparison circuits
in the recorder which in turn control
the angular positions of each of
eleven print wheels. Along their
periphery these wheels contain type
faces for the numerals 0 through 9
as well as blank positions. During
the counter's display time each
wheel turns rapidly to its new print
ing position. This position is deter
mined by the staircase step at which
the wheel's corresponding decade
unit in the counter has stopped.
A print bar in the recorder then
presses the combination of the paper
tape and an inked ribbon against
the print wheels to give a printed
impression which is identical with
ANALOG OUTPUTS
200.200MC
10,008,228 10,008,255
10,008,240 10,008,261
10,008,252 10,008,260
etc.
When recording data of this na
ture by using an analog recorder
with the digital recorder, the ability
of the digital recorder to supply a
voltage that is proportional only to
the final two or three places of each
number is of considerable value,
since it gives the full resolution of
the counter to the analog record. If
the counted sample is large, as in
the above example, resolutions in the
order of 1 part in 107 can be obtained
in the strip record with this feature.
If higher frequencies in the order of
10s are counted with the 10-second
gate of the -hp- Model 524B counter
operating with the Model 525 con
verter, resolutions in the order of
1 part in 10C will be obtained in the
chart. A further feature of this sys
tem is that the strip recorder will
never go off scale, as will be shown
later.
The voltages for the strip recorder
outputs are obtained from staircase
voltages (separate from the counter
staircases) which are generated by
print wheel brushes running against
a commutator. When the print
wheels come to rest to make a print,
the voltage step corresponding to
the wheel position is applied to a
selector switch. This switch applies
the voltages from any three adjacent
wheels or the right-hand two wheels
to a resistive network which adds
the voltages in a 90%-9%-0.9% re
lation. This combined voltage is
then applied to the output terminals.
During the next scan time, when the
Fig. 4. Sample record
made by frequencymodulating 200 me os
cillator at slow rates
with various wave
forms and measuring
and plotting fre
quency change with
recorder-counter com
bination.
200.300MC
5 MIN
© Copr. 1949-1998 Hewlett-Packard Co.
series of readouts like the following
frequency drift data in which only
the last few digits are varying.
•?
Fig. 5. Slide switch on recorder panel
selects desired adjacent columns for ana
log output.
wheels are turning to a new position,
the voltage at the output terminals
is stored in a capacitor so that no
interruption of the output level
will occur.
Even though the analog output is
a step-type voltage, steps normally
do not appear in a strip record when
the 3-column analog output is used.
The reason for this is that the
counter typically samples enough
points that the voltage change be
tween points from the recorder's an
alog output is small. Voltage incre
ments from this output can be as
small as 0.1% of full scale (1 unit
in the third place). At typical strip
recorder lineal speeds these plotted
points overlap or blend together so
that steps do not appear. Figs. 3 and
4 are records which illustrate this
feature.
Steps are more likely to be ob
servable when the right-hand 2column output is used for operating
a strip recorder, since the minimum
voltage increments available are
then 10 times as large as in the 3column case.
ALWAYS ON-SCALE CHARACTERISTIC
Since the analog output is ob
tained by combining staircase volt
ages, the external analog recorder
can not go off scale at any time. This
characteristic occurs because the
staircase voltages always lie between
two limits. If the counted quantity
advances beyond 999, the staircases
will go through their maximum
value and rest at the next reading
which will be an intermediate value.
Similarly, if the counted quantity
decreases through 000, the staircases
will go through their minimum
value and rest at an intermediate
value. Within the limits of the
counter capacity the strip record will
thus always be contained on the
chart, regardless of how much the
count increases or decreases.
Even though the strip recorder
will always be on scale, the total
amount of change in the measured
quantity is still easily determined
from the strip record. Fig. 3, for
example, shows a recording in which
the measured frequency has drifted
downward beyond the full-scale
value of the chart. The total drift is
obtained merely by adding the val
ues of the second curve section to
the first.
The always on-scale feature has
at least three distinct advantages.
First, recordings can be run unat
tended since they can never go offscale. Secondly, data in which a wide
(Cont'd on P. 4)
OPERATION OF THE DIGITAL RECORDER
The new digital recorder has a simple
and straightforward mechanism which
consists of identical sections for each
print wheel. A representation of one of
these sections is shown in Fig. 1. The fol
lowing describes how the section operates.
When the recorder is interconnected
with a counter, the staircase output of
each decade unit in the counter becomes
connected to a comparison circuit in the
recorder. At the same time a staircase
voltage associated with the print wheel
is also applied to the comparator.
During the sampling interval or gate
time in which the counter is accumulating
its count, the comparator circuit is dis
abled. During this time, also, the print
wheel is locked in its last printing position
so that it applies only a fixed step of its
staircase to the comparator.
When the counter gate time is com
pleted, the decade unit staircase from the
counter will rest at a step corresponding
to the count remaining on the decade. As
the gate time ends, the counter applies to
the recorder a command pulse. This com
mand pulse causes three nearly simultan
eous actions within the recorder. First, the
pulse causes a main clutch to engage, and
this causes a shaft on which all print
wheels are mounted to begin rotating.
The print wheels themselves can not yet
rotate, however, because they are locked
in position by a pawl. Second, the re
corder applies an override signal back
to the counter so that the counter can
not begin a new count while the print
ing action is in process.
The third action that occurs from the
command pulse is that the comparator
circuit is activated. If the step applied to
the comparator from the decade staircase
is then not equivalent to that applied
from the wheel staircase, the comparator
energizes a solenoid which releases the
pawl from the print wheel. This permits
a friction clutch on the individual print
wheel to begin rotating the wheel. When
the wheel rotates to its proper position,
such that the two staircase steps applied
to the comparator now correspond, the
© Copr. 1949-1998 Hewlett-Packard Co.
COMMUTATOR
Fig. 1. Basic operating arrangement of
print wheel.
comparator de-energizes the solenoid. The
pawl then locks the wheel in its new
position. This same action has simultan
eously been occurring with each of the
other wheels. At a pre-determined inter
val after the command pulse and after
the wheels are positioned, a cam on the
main shaft presses the print bar, ribbon
and paper against the print wheels, trans
ferring the counter reading to the paper.
The staircase associated with the print
wheel is obtained with a brush and com
mutator arrangement in which each com
mutator segment is connected to a tap on
a fixed resistor. The brush is carried by
the print wheel. When the wheel is in
a locked position, the brush thus supplies
the comparator with a single voltage level
which corresponds to the angular position
of the wheel. When the wheel rotates, the
brush supplies the comparator with step
voltages until the coincident condition
prevails.
The two staircases applied to the com
parator have been designed to be the in
verse of one another. Where the stair
case from the decade unit in the counter
descends from a higher to a lower voltage
as the count increases from 0 through 9,
the staircase from the brush and commu
tator increases as the wheel rotates from
0 through 9. This arrangement makes
(Cont'd on P. 4)
SIX-DIGIT RECORDER
THE DIGITAL RECORDER
(Cont'd from P. 3)
Fig. 6. Drawer is provided in recorder to
receive accordion-folded paper tape.
change may occur such as in warmup curves can be run without danger
of incorrectly anticipating the re
quired full-scale value to which the
recorder should be initially set.
Thirdly, quite rapid variations in
the measured quantity can be plot
ted: the speed is limited mainly by
variations that are sufficiently de
fined by 5 plotted points per second,
i.e., variations in the order of i — 1
cycle per second.
PAPER AND RIBBON
The new recorder is arranged so
that it prints on conventional 3inch adding machine tape and is
further arranged so that two types
of tape can be used. One type is the
standard rolled tape, and the second
is accordion-folded tape (Fig. 6). The
second type is often preferred be
cause it offers convenient access to
any portion of a record. The re
corder is arranged with a drawer
which will accumulate this tape as
it is printed. Either type of tape is
available from -hp-.
The recorder uses a standard type
writer ribbon (medium heavy inked)
on an Underwood-type ribbon spool.
USE WITH -hp- COUNTERS
To interconnect the new recorder
with -hp- counters, a special multiconductor cable is supplied with the
recorder. The counter must then be
modified somewhat to receive this
cable and to make the internal con
nections, but this is easy to do. Modi
fication kits are available for all -hpcounters now in production at nom
inal cost.
The standard Model 560A re
corder is supplied with eleven print
wheels. Since all of these printing
positions may not be required, how
ever, the recorder is normally sup
plied with only six comparator cir
cuits which activate the wheels. The
comparators are constructed in plugin form and extra plug-in units to
activate additional wheels can be ob
tained at extra cost.
RECORDER OPERATION
(Cont'd from P. 3)
for high reliability since the grids of
the comparator tube always see coinci
dence at the same absolute voltage
ACKNOWLEDGMENT
Many members of the -hp- engi
neering department have contrib
uted to the design of the new re
corder. Besides the undersigned, the
electrical team included Duane Mar
shall of the -hp- counter group, while
the mechanical team included con
sulting engineer Harold F. Elliott,
and Francis Berry, Carl J. Clement,
Jr., Everet J. Penn, and Ted Pichel.
—Alan S. Bagley and Ed A. Hilton
SPECIFICATIONS
-hp- MODEL 560A
DIGITAL RECORDER
Accuracy: Identical to that of counter used.
Printing Rote: Controlled by counter; 5
lines/sec, max.
Printing Capacity: 1 1 columns/line. (See
Price).
Required Driving Source: Parallel entry stair
case voltages such as those derived from
• hp- or Dynac, Inc. digital frequency count
ers. Staircase descends from +135 V to
-f-55 V as the count progresses from 0 to
9. Internal impedance of the staircase
source should be approximately 700,000
ohms.
Paper Required: Standard 3" roll or folded
paper.
Line Spacing: Single or double, adjustable.
Analog Output: Output is proportional to the
count indicated by any three adjacent col
umns or by the right-hand two columns of
the print-out in the form of a 1000 step
staircase. Desired columns may be selected
by analog output selector. For example,
if selected adjacent digits were 3, 8, and 6,
output voltage would be 38. ó millivolts (or
.386 ma from galvanometer output); and
99.9 millivolts if adjacent columns were
999.
Output Available: 1 ma for galvanometer
strip-chart recorders. 100 mv for potentio
meter strip-chart recorders.
Power Requirements: 105-125 volts, 60 cycles,
250 watts.
Dimensions: Cabinet Mount: 203/4" wide,
12'/2" high, I6'/2" deep.
Rack Mount: 19" wide, 10'/2" high, 16Vj"
deep.
Weight: Cabinet Mount: 60 Ibs., approx.
Rack Mount: 55 Ibs., approx.
Price: -hp- Model 560A Digital Recorder, in
cludes cable for connecting to -hp- counters
and 6 plug-in comparators.
Cabinet Mount: $1265.00
Rack Mount: $1250.00
Additional plug-in comparators: $25.00
MODIFICATION KITS
(Adapt -hp- counters for use with -hp- 560A
Digital Recorder)
For: -hp- 521A/C: $35.00; -hp- 522B: S35.00;
-hp- 523B: $35.00; -hp- 524B: $125.00.
Factory Installation on New Counters-hp- 521A/C: $45.00; -hp- 522B: $45.00;
-hp- 523B: $45.00; -hp- 524B: $150.00.
Prices f.o.b. Pato Alto, California.
Data subject to change without notice.
© Copr. 1949-1998 Hewlett-Packard Co.
Fig. 2. Relative time relations of opera
tions in recorder.
level, a situation that would not occur
if both staircases progressed in the same
direction.
OPERATING CYCLE
Fig. 2 shows the time relation of the
various operations within the recorder.
When the counter gate closes, the counter
sends the command pulse (B) to the re
corder. This pulse causes the main clutch
to engage, the override signal to be ap
plied to the counter, and the comparator
circuit to be activated (C,D,E). If the
comparator does not see coincidence be
tween the two staircases, it energizes (F)
the wheel solenoid. The wheel then ro
tates to its proper position. After the main
shaft has rotated approximately 8/10
of a revolution, the cam actuates the
printer bar (G) and then advances the
paper and ribbon. The whole cycle re
quires only 0.2 second, after which the
recorder is prepared for another cycle.
If the counter is set for minimum display
time, it will have completed another
count in the last 40 milliseconds of the
0.2 second cycle, so that another printing
cycle can begin immediately. A maximum
of 5 printed lines per second can thus
be obtained.